1. Technical Field of the Invention
The present invention relates to a method and an apparatus for recognizing the shape of a road on which the vehicle travels.
2. Related Art
Methods of calculating a lane-probability instantaneous value are well known. The term lane probability refers to a probability that a target to be recognized ahead of the vehicle is present on the same lane. A lane-probability instantaneous value is calculated from a curve radius of the road where the vehicle travels in order to make a determination on an object to be controlled. The curve radius is obtained from a position (distance and lateral position) of a target ahead of the vehicle that has been detected by a sensor, a state of turn of the vehicle that has been obtained based on a steering angle and a yaw rate, and a speed of the vehicle. A lane-probability instantaneous value calculated in this way is corrected and applied such as with a predetermined filtering process to calculate a lane probability, based on which a preceding vehicle is selected.
However, the state of turn of the vehicle is usually not in conformity with the shape of the road on which an actual object to be controlled travels. To take measures against this, a Patent Document 1 (JP-B-3417375), for example, discloses a technique for calculating a lane probability. According to the technique, the shape of the road the vehicle travels is recognized to correct a curve radius R of the turn of the vehicle and to correct a lane-probability instantaneous value. The corrected lane-probability instantaneous value is applied such as with a predetermined filtering process to calculate a lane probability, based on which a preceding vehicle is selected.
However, the calculation according to the technique of conventional art mentioned above is based on the estimation of a road edge that matches the shape of the road. Therefore, the technique is unlikely to provide a correct estimation when the vehicle does not travel along the shape of the road, such as when the vehicle travels through an interchange, a ramp, i.e. on-ramp or off-ramp, a climbing lane or the like, or when the vehicle, such as a bus, is going to stop at a bus stop on an expressway.
For example, as shown in FIG. 11, a road of left-hand curve on which the vehicle travels may be connected with a road of right-hand curve. In this case, when a curve radius (curvature radius) R calculated based on the recognized road shape is corrected, for a curve radius R calculated on the vehicle side, the corrected curvature radius R is not in conformity, after all, with the shape of the road the vehicle travels. Thus, even when the shape of the road is recognized correctly on the vehicle side, the correction of the curvature radius R is likely to impair correct road shape recognition in a situation as shown in FIG. 11.
Further, according to the technique disclosed in this Patent Document 1, it is determined whether an object is a moving object or a stationary object in recognizing the shape of the road. Then, the stationary objects are connected and grouped for the recognition of a road edge.
The conventional art mentioned above may encounter a problem that roadside objects are not detected due to the presence of a preceding vehicle or that the absolute number of roadside objects is small. Accordingly, a road edge is not calculated more correctly and with good frequency, and thus the shape of the road is unlikely to be recognized more correctly.
Further, according to the conventional art mentioned above, stationary objects that are not roadside objects may be targeted for grouping, or a base point of the grouping may be incorrect. Thus, grouping of roadside object groups is unlikely to be performed with good accuracy. As a result, a road edge is not calculated more correctly and with good frequency, and thus the shape of the road is unlikely to be recognized more correctly.
On the other hand, a Patent Document 2 (JP-B-3427809) suggests a method of recognizing a road on which the vehicle travels. Specifically, in the method disclosed in the Patent Document 2, segmentized measurement data is sorted in the order of, angle to remove unnecessary data based on the shape of segment and to remove segments located in the vicinity of moving objects. Then, the segments effective for recognizing the shape of the road are grouped clockwise and counterclockwise. Further, a farthest segment, if it is doubtful, is removed. Then, road edges are recognized based on a roadside object group (left) and a roadside object group (right).
However, according to the conventional art mentioned above, the base point for grouping roadside objects may sometimes be incorrect, and thus grouping of roadside object groups is unlikely to be performed with good accuracy. As a result, a road edge is not calculated more correctly and with good frequency, and thus the shape of the road is unlikely to be recognized more correctly.
Further, the conventional art mentioned above may encounter a problem that roadside objects are not detected due to the presence of a preceding vehicle or that the absolute number of roadside objects is small. Accordingly, a road edge is not calculated more correctly and with good frequency, and thus the shape of the road is unlikely to be recognized more correctly.
In addition, the shape of the road on which an actual object to be controlled travels is unlikely to be in conformity with the state of turn of the vehicle. In this regard, a Patent Document 3 (JP-A-2001-328451) suggests a technique for calculating a curve radius of a road based on a stationary object as well when the stationary object is present on the road. Then, a curve radius based on the vehicle is corrected using the curve radius based on the stationary object. The corrected curve radius is used for calculating a lane-probability instantaneous value which is then used for calculating a lane probability. Then, based on the lane probability, a preceding vehicle is selected.
In this way, generally, in recognizing the shape of a road, stationary objects are recognized as mentioned above and a curve radius is calculated based on the stationary objects. However, for example, it is sometimes difficult to detect stationary objects due to the presence of a preceding vehicle, or the absolute number of stationary objects may be small. For this reason, stationary objects do not necessarily contribute to accurately calculating a curve radius, and thus the shape of the road is not necessarily calculated correctly and with good frequency.